Beneficiation of phosphate ores



June 1s, 196s MQ F. .mE-,BLE 3,388,793

BENEFICIATON OF PHOSPHATE ORES Filed Nov. 26, 1965 24J .De fat'er (one o inf/ow [alec/fiona? Jec 2": 'are United States Patent O 3,388,793 BENEFICIATION F PHOSPHATE GRES Merton F. Dibble, Lakeland, Fla., assignor to International Minerals & Chemical Corporation, a corporation of New York Filed Nov. 26, 1965, Ser. No. 509,934 12 Claims. (Cl. 209-3) ABSTRACT 0F THE DSCLSURE A deslimed liberated phosphate ore is beneficiated by a process which includes first classifying the same at about 14 to 42 mesh to produce a fine fraction and a coarse fraction. The coarse fraction is subjected to a coarse rougher flotation operation in the presence of an anionic reagent to produce a coarse rougher concentrate and a coarse rougher tail. The coarse rougher tail is classified at about 24 to 28 mesh to produce a discard second fine fraction and a second coarse fraction, which is comminuted and subjected to fine rougher flotation operation in the presence of an anionic reagent to produce a fine rougher concentrate and a discard fine rougher tail. The fine rougher concentrate and coarse rougher concentrate are finally scrubbed with an acid and subjected to a flotation operation in the presence of a cationic reagent to yield a discard cationic tail and a final cationic concentrate.

This invention relates to the beneficiation or concentration of phosphate ores and, more particularly, this invention relates to a process for `beneliciating a phosphate ore to obtain a high grade phosphate concentrate.

Early practices in the concentration of phosphate ores comprising apatite or fluorapatite and siliceous gangue entailed reagentizing the liberated finely divided ore with an anionic reagent effective to selectively coat a portion of the surfaces of the phosphatic particles present, followed by concentration of the reagentized ore by froth floation to provide a phosphate concentrate as a froth product and a silica tail as a depressed or sink product. At acceptable levels of recovery, particularly from relatively low-grade ores, the grade of the concentrate was objectionably low.

An alternative procedure known to the early art embraced reagentizing the liberated phosphate ore with a cationic reagent effective to selectively coat at least a portion of the surfaces of the silica particles, followed by froth flotation to produce a silica tail as a froth product and a phosphate concentrate as a depressed or sink product. Such a procedure likewise failed to afford a concentrate of satisfactory grade and recovery.

Accordingly, the phosphate industry, and in particular the Florida phosphate industry, resorted to a combined process wherein a deslimed phosphate ore is sized by means of classifiers, screens, trommels, hydroseparators and the like, to provide a line fraction which is amenable to wet beneticiation, eg., flotation, and a coarser fraction which is generally considered to be too coarse to be satisfactorily beneficiated by flotation. The sizing is usually carried out such that the line fraction has a size range of about 35 mesh and coarse fraction has a size range of about +35 mesh. It will be understood that the particle size designations used throughout this application relate to Standard Tyler screen sizes with the plus references meaning particles larger than a screen of the stated size and minus references meaning particles that pass through a screen of the stated size.

The 35 mesh line fraction is first subjected to a rougher flotation in the presence of an anionic reagent to produce a rougher concentrate comprised of reagentbearing phosphate minerals and silica, which is treated 3,388,793 Patented June 18, 1968 ice with a mineral acid to remove the reagent coating, and the essentially reagent-free rougher concentrate is then subjected to a second flotation in the presence of a cationic reagent effective to selectively coat the silica particles so as to produce a final phosphate concentrate product and a silica tail. The combined process is described in detail in U.S. Patent No. 2,293,640 of Crago. Modifications of the Crago process which treat finely divided ore and embrace the same general sequence of steps are described in a plurality of subsequently issued U.S. Patents, including: Duke, 2,461,813; Duke, 2,666,842; Houston, 2,706,558; Hunter, 2,750,036; and Duke, 2,753,997. Reference is made to the disclosures of the aforementioned patents for a more detailed teaching with respect to the concentration of phosphatic minerals with anionic and cationic reagents, and methods for the removal of such reagents from the concentrates produced.

The |35 mesh coarse fraction from the sizing step has always presented a serious problem to the Florida phosphate industry in that no process has been devised that produces the optimum in recovery and product grade. This fraction has been treated by a variety of techniques, all of which produce approximately the same recovery and product grade. As for example, U.S. Patent No. 3,032,197 of Northcott describes a process wherein the coarse l-j-35 mesh fraction is conditioned with an anionic flotation reagent and thereafter concentrated in a spiral concentration apparatus, such as a Humphrey Spiral, to produce a spiral rougher concentrate and a spiral rougher tail. The spiral rougher tail is subjected to scavenger beneficiation in flotation cells (or in scavenger spirals) to produce a scavenger concentrate, which is combined with the rougher spiral concentrate, and a scavenger tail, which is discarded with the general mill tails. The combined rougher spiral concentrate and scavenger concentrate are then subjected to a cleaner flotation in the presence of a cationic reagent to produce a float product, which is combined with the general mill tails, and a sink or depressed product, which is combined with the final concentrate product produced from the fine 3.5 mesh fraction.

Such a commercial process is effective for recovering from about to 95% of the phosphate values from ores containing from about 30 to 50% BPL (bone phosphate of lime). However, the product of the spiral circuit frequently contains an excessive quantity of impurities, which are primarily silica with minor amounts of other acidinsoluble materials and are known in the art as insoL The presence of locked insol in phosphatic particles is one cause of a relatively high insol content in the product of the spiral circuit. Coarse insol is also present due to the non-selectivity of the spiral circuit. As a result of the insol, it is difficult to obtain from the +35 mesh fraction a product of satisfactory grade, i.e., a product having an accepta-ble weight for its BPL value. This is of importance to the phosphate industry since a phosphatic material of relatively high BPL and low impurity content is required for the production of fertilizers, e.g., superphosphate and triple superphosphate, and price penalties are imposed when impurities are present in excess of certain minimum fixed percentages.

It has been found that the silica and other acid-insoluble materials are prevalent in the portion of the +35 mesh fraction flotation tailing, having a particle size finer than about 28 mesh. More specifically, these materials comprise the major part (e.g., about 60 to 90 wt. percent) of the -28 +35 mesh portion, while these materials are only a minor part (e.g., about 10 to 40 wt. percent of the l6 +28 mesh portion. Consequently, the +28 mesh portion contains the major portion, i.e., about 75 to of the tailing phosphate values. The insoluble materials are present in the -16 +28 mesh portion as locked particles, the bulk of which have a size within the range of about 48 to 65 mesh. The screen analysis of a coarse anionic flotation tailing of the -16 +35 mesh fraction of a typical Florida phosphate which is set forth in Table I clearly demonstrates this distribution of the silica and other insoluble materials.

TABLE I Cumulative, BPL, Cumulative Mesh Wt. Percent Wt. Percent Percent BPL, Percent Content 16. 6 16. 6 64. 62 46. 2 -16+20 6. 9 23. 5 51. 56 61. 4 -20+28 20. 7 44. 2 25. 23 84. 0 Z8-H55- 24. 9 69. 1 9. 35 94. 0 35+48 20.0 89,1 3.71 97.4 -48-l-t5- 7. 7 96. 8 3. 21 98. 5 -65 3. 2 100. 0 6. 13 100.0

In accordance with this invention, the coarse flotation tailing is sized at about 28 mesh so as to obtain a frac tion consisting substantially of the larger particles and containing a large portion of the BPL value of the coarse flotation tailing with a minimum of weight retention. A screen analysis of a coarse anionic flotation tailing of the -16 +35 mesh fraction from a typical Florida phosphate rock, which was subsequently screened at 28 mesh on a wedge bar screen, is given in Table II.

The oversized fraction, i.e., the +16 +28 mesh fraction, is then ground to liberate the locked or embedded insoluble materials and to comminute the coarse particles which would otherwise be too large for subsequent flotation. The product from this grinding action is then wet concentrated or beneciated to recover a phosphate product of high quality.

It is, therefore, a primary object of this invention to provide a method for the wet beneficiation of phosphate ores whereby high recoveries of phosphate values are realized. f

Another' object of this invention is to provide a method for the beneflciation of phosphate ores whereby a high grade phosphate concentrate is obtained` Another object of this invention is to provide a beneficiation method for obtaining a phosphate product having a low insol content.

Still another object of this invention is to provide a method for the wet beneciation of phosphate ores whereby a high proportion of the phosphate values are recovered.

A further object of this invention is to provide an improved method for the wet beneficiation of a +35 mesh phosphate ore fraction.

These and further objects of this invention are accomplished by treating the phosphate matrix as it is mined in accordance with conventional procedures to remove the pebble fraction, i.e., the largest material which is sold without any further treatment, and slime material. The remaining material is then sized to separate the materials of a size amenable to flotation from the material of a size which is generally considered to be too coarse to be satisfactorily beneficiated by flotation. Due to the nature of the phosphate ore as obtained from the natural deposit, it' happens that the fine material obtained from this sizing step is substantially free of locked or embedded silica, while the coarse material contains embedded silica in a substanial portion thereof, with the silica being present in the larger of the coarse material as locked particles. The line fraction is treated in accordance with conventional procedures.

The coarse phosphate particles are initially subjected to a coarse rougher wet concentration, e.g., flotation, in the presence of an anionic reagent to produce a coarse rougher concentrate and a coarse rougher tail. The coarse rougher tail is sized to separate the larger particles, i.e., those which contain the major portion of the coarse rougher tail phosphate values with a major portion of locked or embedded silica and a minor amount of free silica, from the smaller particles. Since the smaller particles contain a minor amount of the phosphate values of the coarse rougher tail and the major portion of the free silica, they are discarded. The larger particles are comminuted so as to liberate the locked Silica and to reduce the size of the particles so that they are amenable to flotation. The comminnuted phosphate particles are then subjected to a fine rougher wet concentration, e.g., flotation, in the presence of an anionic reagent to yield a fine rougher concentrate and a fine rougher tail which is discarded. The fine rougher concentrate is scrubbed to remove the anionic reagent and is finally subjected to wet concentration, eg., flotation, in the presence of a cationic reagent to yield a final concentrate product, The coarse rougher concentrate is also scrubbed and subjected to wet concentration in the presence of a cationic reagent. The coarse rougher concentrate may `be combined with the fine rougher concentrate before it is scrubbed and subjected to cationic flotation, or it may be separately treated.

More specifically, the method of this invention as applied to the present processing of pebble phosphate ore, such as is obtained in Florida, comprises the transfer in slurry form of the phosphate matrix as it is mined from the natural deposit. This slurry contains sizeable amounts of silica, clay and miscellaneous gangue materials in addition to the phosphate. The ore is subjected to a preliminary washing and screening operation which produces a pebble product containing all of the +114 or +16 values.

The remaining material, i.e., -14 or -16 mesh material, is processed to give maximum recovery of the granular material and substantially complete removal of the slime material, which would adversely affect the subsequent concentration process if allowed to remain. Separation of the slime material may be accomplished in a number of ways, as by a hydro-separation or hydrocyclone process. The overflow from the desliming operation is withdrawn and sent to a settling or slime pond. This overflow is made up chiefly of suspended clay and extremely fine particles of phosphate, i.e., particles of a suflicient degree of fineness that they could not be economically recovered at any subsequent step of the process. This separation is commonly made at approximately 150 or 200 mesh. The coarser fraction, which may have a size range of at least -14 +200 mesh but is usually about -16 +150 mesh, is separately withdrawn from the desliming section and is sized further, as by hydraulic classification or screening, at about 32 to 42 mesh, usually at about 35 mesh. The fine fraction (e.g., -35 +150 mesh) is subjected to froth flotation operations in accordance with conventional procedure and the coarse fraction (e.g., -16 +35 mesh) is treated in accordance with this invention.

The tine -35 +150 mesh fraction is first reagentized employing any of the standard anionic or negative ion flotation agents known to the art so as to selectively float the phosphate values of the ore. The particular anionic reagent utilized in the froth flotation of the phosphate ores does not constitute the essential feature of this nvention which is operable with and contemplates all such reagents. Representative conventional anionic reagents comprise fatty acids or fatty acids soaps, particularly mixed fatty acids or soaps thereof; fatty acids derived from natural 'sources such as tall oil soaps; fatty acids or soaps oi acids derived from animal and vegetable fats;

esters of inorganic acids with high molecular weight alcohols; and the like. Conventionally, such anionic reagents are applied in solution or in a dispersion in a carrier medium such as a hydrocarbon oil, normally kerosene or fuel oil. One widely used specific reagent in cornbination comprises about one to three parts tall oil, about one to four parts kerosene, and about one to four parts Bunker C fuel oil. Such a reagent is used in admixture with sodium hydroxide in an amount requisite to raise the pH to within the range of from about 7.0 to about 9.0.

The reagentized ore is subjected to froth flotation employing any of the standard flotation equipment known to the art. It will be apparent that a battery of units in parallel or in `series may be employed for the flotation. Thus, for example, the anionic flotation can be accomplished in a battery of anionic flotation cells to produ-ce an overflow which in turn is processed further in a second battery of cleaner anionic flotation cells. The flotation is effective to remove as an overflow concentrate a substantial amount of the phosphate values of the ore together with some of the finer silica particles. The tail, predominating in silica and containing a minor amount of phosphate, is discarded.

The anionic reagents are removed from the phosphaterich overflow concentrate employing such standard prior art means as scrubbing with water, or more desirably with a mineral acid such as sulfuric or hydrochloric acid, eg., a 98% sulfuric acid solution. rhe term scrubbing as used in the wet mineral processing art means agitation of the solids in slurry form, generally in a solids content of about 45% to about 75% solids. In conformance with recognized procedures, the anionic concentrate slurry may be partially cle-watered before the scrubbing thereof in order to permit a more efficient removal of the anionic reagent. After the phosphate concentrate is scrubbed, the acid solution is removed in dewatering and washing steps.

The phosphate-rich concentrate is reagentized with a cationic reagent following the removal of the anionic reagent. Again, any of the cationic or positive ion flotation reagents known to the art may 'be used. Such reagents include the higher aliphatic amines and their salts with water-soluble acids; the este-rs of amino alcohols with high molecular weight fatty acids and their salts with water-soluble acids; the higher alkyl-O-substituted isoureas and their salts with water-soluble acids; the higher aliphatic quaternary ammonium bases and their salts with Water-soluble acids; the higher alkyl pyridinium water-soluble acids; and the like. Specific examples of such cationic reagents include N-dodecylamine, N-hexadecylamine, and lauryl fatty diamine and soya fatty diamine acetate. As hereinbefore described with respect to the anionic flotation stage, the cationic llotation step may consist of a battery of rougher cells employed in conjunction with a second battery of cleaner cells. This flotation yields a first underflow phosphate product and an overflow silica tail which is discarded.

The coarse -16 +35 mesh fraction is treated in accordance with this invention by first being reagentized with an anionic flotation reagent as hereinbefore characterized. The reagentized coarse fraction is then subjected to a coarse rougher flotation, as by utilizing a battery of flotation units in parallel or in series as herein before described with respect to the flotation of the -35 +150 mesh `fraction this flotation is effective to produce an overflow coarse rougher concentrate of phosphate values substantially free of embedded silica and an underflow coarse rougher tail of phosphate values containing embedded silica.

The coarse rougher tail fraction is then introduced into a sizing section where it is sized at about 24 to 28 mesh, usually at about 28 mesh, so as to remove the larger particles from the coarse rougher tail. It is preferred that the sizing be Iconducted with a dewatering type sizing device, e.g., a stationary or vibrating screen or an open top cyclone, since it has been found that the reagentized phosphate particles that have a size less than 28 mesh will tend to be concentrated in the oversize or productyielding fraction. For example, in referring to the analysis of the -48 +65 mesh fraction given in Table II, a 9.51% BPL oversize and a 2.11% BPL undersize obtained from a 5.06% BPL feed. Thus, about 70% of the BPL values of the -48 +65 mesh fraction is recovered even though the fraction is finer overall than the size split for the sizing circuit. The indication is that if a phosphate particle is reagentized but liner than the size of the split desired, it will still report to the coarse or oversize fraction due to the presence of the hydrophobic reagent. This sizing of the reagentized tailing therefore actually functions as a concentration step. The undersize portion of the coarse rougher tail is discarded because these particles have a relatively low phosphate value for their weight.

The oversize fraction, i.e., the -16 +28 mesh fraction, is introduced into a grinding section where it is ground to comminute the coarse particles which are considered to be too large for flotation to a size amenable to flotation and to liberate substantial amounts, e.g., 70 to 90%, of the locked silica. The grinding operation is regulated so that the outflow contains a substantial amount, eg., about 40 to 80%, of material having a size of about -24 or -32 mesh. More specifically, the grinding operation is regulated to produce about 60 to 70% of -28 mesh material. The comminution may be performed dry or wet; however, since the subsequent step is a wet step and since wet comminution produces the best results with a minimum production of material which is too fine, a wet comminution is preferred. The ore may be comminuted in any conventional apparatus of the art, including, without limitation, grinders, rod mills, hammer mills, ball mills, cage mills, jaw crushers, and the like.

During the comminution as in a cage mill, some extremely fine material is produced and more slimes are further liberated from the material. The mill discharge, thereafter, is preferably introduced into a dewatering device so as to separate the extremely fine material and slimes, as well as to remove water from the mill discharge to permit a more efficient operation of the subsequent steps. The underflow from the dewatering device is rereagentized with an anionic or negative ion flotation agent as described above. This anionic reagent may be the same as or different from the anionc reagent utilized in the coarse rougher flotation, but it will be evident that for simplicity, i.e., anionic reagent recovery, it is preferred that the same reagent be used in the two rougher flotation steps. The re-reagentized material is then subjected to a fine rougher flotation operation, preferably using a battery of flotation units in parallel or in series. The fine rougher flotation operation is effective to separate as an overflow concentrate the major portion of the phosphate values of the coarse rougher flotation tail with a minor amount of the silica, while the major portion of the silica content of the coarse rougher flotation tail is removed with a minor amount of phosphate as an underflow line rougher flotation tail.

The anionic reagents are removed from the fine rougher concentrate by scrubbing it, as with a mineral acid. The scrubbed fine rougher concentrate is nally subjected to flotation in the presence of a cationic reagents as hereinbefore characterized with respect to the fine -35 +150 mesh fraction. This flotation yields an underflow second phosphate product concentrate and an overilow silica tail which is discarded.

The coarse rougher flotation concentrate, which predominates in phosphate and hence contains only a minor amount of silica, is scrubbed, preferably with a mineral acid solution such as 98% sulfuric acid solution, to remove the anionic reagents therefrom and is subjected to a flotation in the presence of a cationic flotation reagent as described above to produce a third phosphate product concentrate.

It will be evident that the -35 +150 mesh fraction obtained from the 35 mesh sizing section, the -16 +28 mesh fraction obtained from the sizing of the coarse rougher flotation tail, and the coarse rougher flotation concentrate may be individually treated to obtain three eparate concentrate phosphate products, which may be kept separate or be combined, or that these three fractions may be combined at appropriate stages in their processing so that only one acid scrubbing and cationic flotation operation need be used. More specifically, the -35 +150 mesh fraction may be combined with the -16 +28 mesh fraction upon its discharge from the mill (and dewatering step) so that these two fractions are simultaneously treated with an anionic reagent and subjected to the fine rougher anionic flotation to produce a combined line rougher anionic concentrate, which is then combined with the course rougher concentrate so that the three fractions are simultaneously scrubbed with an acid and subjected to the cationic flotation.

The invention is generically applicable without limitation to phosphate ores amenable to wet concentration. Specific ores contemplated include Florida pebble concentrate, the various Tennessee phosphates, and the various foreign phosphate ores such as Moroccan phosphates. The invention can effectively be utilized with all wet concentration procedures including, without limitation, conventional flotation, skin flotation, spiral processing, tabling, belt concentration, and the like. The process of this invention is particularly applicable, however, to froth flotation operations which are conventionally utilized in the beneflciation -of Florida pebble phosphate rock.

This invention might best be understood by reference to the accompanying drawing, which is a schematic flowsheet of a commercial Florida phosphate ore benellciation wherein a process comparable to that described in the Crago patent is utilized. Reference is made to the accompanying drawing, wherein it is shown that in accordance with conventional procedure, the Florida phosphate matrix is first passed into washing and sizing section 10 to attain a +16 mesh pebble phosphate product which is sold without further processing. The -16 mesh underflow from washing and sizing section 10 is substantially deslimed in desliming section 12, which uses conventional desliming apparatus such as desliming cones. The -150 mesh slime-containing overflow from desliming section 12 is sent to waste. The 16 +150 mesh deslimed ore comprises the underflow from desliming section 12 and is separated in sizing section 14, which is of conventional design, into a -16 +35 mesh coarse fraction and a -35 150 mesh fine fraction.

The -16 +35 mesh coarse fraction is treated in accordance with the process of this invention by first being passed into conditioning tank 16 where it is appropriately conditioned with a conventional anionic froth flotation reagent such as tall oil, fuel oil and kerosene, in admixture with a base such as sodium hydroxide in an amount to raise the pH to the range of about 7.0 to about 9.0. The conditioned material passes from conditioner 16 into a bank of coarse rough flotation cells 18. Coarse rougher flotation cells 18 yield a coarse rougher flotation concentrate comprising essentially phosphatic materials substantially free of embedded silica and a coarse rougher flotation tail comprising phosphatic materials containing a substantial amount of embedded silica and other insolubles.

The coarse rougher flotation tail is passed into sizing section 20, preferably a wedge bar type screen, to separate the portion of the coarse rougher flotation tail which contains a large portion of the BPL value thereof with a minimum of weight retention. This sizing operation is preferably conducted at about 28 mesh to obtain an oversize fraction consisting ot' phosphaiic materials` containing a minor amount of embedded and free silica. The materials passing through the screen are discharged to general mill tails.

The oversize fraction is passed into mill 22 where the locked insoluble materials are liberated from the oversize fraction while it is ground to a size to make it amenable to froth flotation. This grinding is usually done to produce a product containlng from about 60 to 70% of -28 mesh material. The mill discharge is sent into a conventional dewatering device, e.g., dewatering cone 24, to obtain an overflow which is sent to a settling pond fory eventual plant re-use and an yunderflow product. The underflow `from dewatering cone 24 is then sent into conditioning tank 26 where it is re-reagentized with an anionic reagent. The conditioned ore is then passed from conditioner 26 into a bank of fine rougher flotation cells 28 to yield a fine rougher flotation cell which is discarded and a fine rougher flotation concentrate.

The concentrate from tine rougher flotation cells 28 is combined with the concentrate from coarse rougher flotation cells 18 and the combined concentrates are passed into acid scrubbing section 30 for treatment with a mineral acid, such as a 98% vsulfuric acid solution, to remove the reagent coating. The acidscrubbed anionic reagent-free, rougher flotation concentrate is finally subjected te cationic flotation in a bank of flotation cells 32. If desired, the acid-scrubbed rougher flotation concentrate may be conditioned with the cationic reagent in a conditioner before it is introduced into flotation cells 32. Flotation cells 32 produce a froth product comprising essentially a silica tail which is discharged to general mill tails, and a sink product consisting of phosphatic materials which constitutes the final concentrate.

The -35 +150 mesh fine fraction (obtained from sizing section 14) is treated in accordance with conventional procedure. That is, it is introduced into settling tank 34 to remove excess water which is removed as overflow and is sent to a settling pond for eventual plant reuse. The dewatered ore is removed from settling tank 34 as an underflow and is then conditioned with an anionic reagent, subjected to an anionic flotation so as to produce a concentrate which is scrubbed with an acid to remove the anionic reagent and the scrubbed concentrate is then subjected to cationic flotation, If desired, the underflow from settling tank 34 may be combined with the coarse rougher flotation tail of the -16 +35 mesh coarse fraction in conditioner 26 for treatment with this fraction, as illustrated.

The following example is included in order to more fully describe the process af this invention:

EXAMPLE A phosphate rock of the type found in the phosphate pebble fields of Florida, washed and screened to about -16 +150 mesh, is initially subjected to a screening operation at 35 mesh to yield 271 t./h. (tons per hour) of a -16 +35 mesh coarse fraction (40% BPL) and 812 t./h. of a -35 +150 mesh fine fraction (22% BPL).

The -16 +35 mesh fraction is conditioned with 5.0 lb./ ton of an anionic reagent (2.3 lb./ton of a soap sold under the trade name of Tall Oil Skimmings by West Virginia Pulp and Paper Co., 1.3 lb./ton of Bunker C fuel oil and 1.4 lb./t0n of kerosene) in admixture with 1.1 lb./ ton of sodium hydroxide. The reagentized -16 +35 mesh fraction is subiected to a coarse rougher flotation to yield a coarse rougher concentrate of 126 t./h. (65% BPL) and a coarse rougher tail of 145 t./h. (18.6% BPL).

The coarse rougher tail is sized at 28 mesh to produce 91 t./h. of a -28 mesh discard fraction (5% BPL) and 54 t./h. of a +28 mesh fraction (40% BPL). The +28 mesh fraction is comminuted in a cage mill to -28 mesh. The rod mill discharge is introduced into a dewater ing cone to yield 5 t./h. of overflow (45% BPL) which is sent to a settling pond for eventual plant reuse and 49 t./h. of an underflow (40% BPL).

T he dewatering cone underflow is combined with the -35 +150 mesh fraction and the combined fractions are conditioned with 5 lb./ ton of an anionic reagent as hereinbefore described in admixture with 1.1 lb./ton of sodium hydroxide. The reagentized combined fractions are then subjected to a line rougher notation to yield 585 t./h. of a discard tail (5.3% BPL) and 276 t./h. of a ne rougher concentrate (65% BPL).

The tine rougher concentrate is combined with the coarse rougher concentrate and the combined concentrates are scrubbed with a 98% sulfuric acid solution to yield 402 t./h. of an amine flotation feed (65% BPL). The amine dotation feed is finally subjected to flotation in the presence of an amine flotation reagent, sold by American Cyanamid Co. under the trade name of Aerornine 3037, to yield a discard amine flotation tail of 52 t./h. (14% BPL) and 35i() t./ h. of a product concentrate (72.6% BPL).

The total BPL recovery of the above process is 88%, as compared to recoveries of about 88% obtained in conventional processes.

Although this invention has been described with respect to specific embodiments it will be apparent that obvious modifications may be `made by one skilled in the art without departing from the invention as dened by the appended claims. TFor example, while the method has been described as a continuous process it will be apparent that it also can be practiced as a batch process.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for benefciating a deslimed phosphate ore including ne phosphate particles substantially free of embedded silica and coarse phosphate particles containing embedded silica in a substantial portion thereof, the larger of said coarse phosphate particles containing a minor amount of said embedded silica and a major amount of the phosphate values of said coarse phosphate particles, which comprises separating said coarse phosphate particles from said fine phosphate particles, subjecting said coarse phosphate particles to a coarse rougher Wet concentration in the presence of an anionic reagent to yield a coarse ro-ugher concentrate and a coarse rougher tail, separating from said coarse rougher tail the particles containing the major amount of the phosphate values and comminuting the same, subjecting said comminuted particles to a fine rougher wet concentration to yield a ne rougher concentrate and a discard tine rougher tail, treating said `fine rougher concentrate to remove anionic reagents therefrom and subjecting said dereagentized ne rougher concentrate to a final wet concentration in the presence of a cationic reagent to yield a discard tail fraction and a concentrate product fraction.

2. A process for beneficiating a phosphate ore fraction containing particles of a mesh size of from about 14 to about 42 mesh, which comprises subjecting said ore fraction to a coarse rougher wet concentration in the presence of an anionic reagent to produce a coarse rougher concentrate and a coarse rougher tail, classifying said coarse rougher tail at about 24 to 28 mesh so as to obtain a large particle fraction and a ne particle fraction, com- -minuting said large particle fraction, subjecting said comminuted fraction to a tine rougher wet concentration in the presence of an anionic otation reagent to produce a fine rougher concentrate and a discard fine rougher tail, scrubbing said fine rougher concentrate to remove anionic reagents therefrom, and subjecting said scrubbed ne rougher concentrate to a final wet concentration in the presence of a cationic reagent to produce a discard tail fraction and a final concentrate fraction.

n'. un;

3. A process in accordance with claim 2 wherein said wet concentration steps comprise otation operations.

4. A process in accordance with claim 3 wherein said large particle fraction is comminuted to about 40 to 88% having a size of about -24 to -32 mesh.

5. A process in accordance with claim 4 wherein a dewatering type sizing device is utilized for classifying said coarse rougher tail before the comminution step.

6. A process in accordance with claim 5 wherein a screen is utilized for classifying said coarse rougher tail.

7. A process in accordance with claim 6 wherein said phosphate ore fraction contains particles of a mesh size of from about 16 mesh to about 35 mesh.

8. A process in accordance with claim 7 wherein said coarse rougher tail is classified at about 28 mesh.

9. A process in accordance with claim 8 wherein said large particle fraction is comminuted to about 60 to 70% of -28 mesh material.

10. A process in accordance with claim 9 wherein a wedge bar type screen is utilized for classifying said coarse rougher tail.

11. In a process for beneciating a deslimed phosphate ore consisting of particles having a size of less than about 16 mesh which includes classifying said ore at about 35 mesh to produce a rst ne fraction and a first coarse fraction, subjecting said first tine fraction to wet concentration in the presence of an anionic reagent to produce a discard anionic tail and an anionic concentrate, scrubbing said anionic concentrate to remove anionic reagents therefrom, and subjecting said scrubbed anionic concentrate to wet concentration in the presence of a cationic reagent to produce a cationic concentrate and a discard cationic tail; the improvement which comprises subjecting said coarse fraction to a coarse rougher wet concentration in the presence of an anionic reagent to produce a coarse rougher concentrate and a coarse rougher tail, classifying said coarse rougher anionic tail at about 28 mesh with a dewatering type of screening device to produce a second tine fraction and a second coarse fraction, comminuting said second coarse fraction to about 40 to 80% of about -24 to -32 mesh material, subjecting said comminuted material to a ne rougher wet concentration in the presence of an anionic reagent to produce a fine rougher concentrate and a discard fine rougher tail, scrubbing said ne rougher concentrate to remove anionic reagents therefrom, and subjecting said scrubbed tine rougher concentrate to wet concentration in the presence of a cationic reagent to produce a discard cationic tail. and a cationic concentrate.

12. A process in accordance with claim 11 wherein said coarse rougher concentrate is scrubbed to remove anionic reagents therefrom, and said scrubbed coarse rougher concentrate is subjected to wet concentration in the presence of a cationic reagent to produce a discard tail and a cationic concentrate.

References Cited UNITED STATES PATENTS 2,668,617 2/1954 Houston 209-166 X 2,931,502 4/1960 schoeld 209-166 X 3,032,197 5/1962 Northcoa 209-166 3,099,620 7/1963 Adam 209-166 X 3,145,163 8/1964 nancy 209-12 3,225,923 12/1965 Lawver 209-12X HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner. 

